It is a cruel bit of irony that eBay’s current woes come just as the e-commerce pioneer was proving that it still had a business worth stealing.

EBay’s shares have shed nearly 10% over the past two trading sessions, starting their retreat when former subsidiary PayPal reported late last week that payment volumes associated with the eBay Marketplace business grew by only 3% year over year during the third quarter. Because PayPal is believed to still handle the vast majority of transactions on eBay, analysts took the disclosure...